The present invention relates to electric motors, and more particularly to alternating current induction electric motors. In one form, the present invention is embodied in a direct drive motor wherein the output or drive shaft is fixedly attached through a hub to an annular, disc-like rotor member which is axially spaced apart from and lies between a pair of magnetic pole pieces, each having distributed two-phase windings lying in transverse slots in the pole pieces or stator bodies. The pole piece may be a single piece directed opposite to one face of the disc or rotor, or two pole pieces may be provided, each facing the other with the disc or rotor disposed therebetween. In either case, a magnetic return path is provided by a transverse slotted, so-called, return element of a permeable material. The function of this element may be carried out by a transverse slotted return element per se, or may be carried out by the other stator or pole piece, with each stator then serving as the return piece for the oppositely disposed stator in such a construction.
Various types of electric motors are known in the prior art, certain types of prior art motors having been customarily chosen for or particularly adapted to one or more advantageous uses, depending on the characteristics of the motor. Thus, in some instances, starting torque is not important and it is only required that the electric motor run in continuous use at a speed which is equal to or proportional to the frequency of an applied alternating current, such motor being referred to as a synchronous induction motor. In other cases, other characteristics desired for electric motors may be provided for the use in question. Included among such motors are so-called squirrel cage induction motors, so-called shaded pole motors, linear motors or linear actuators. Direct current (d.c.) motors or three phase (a.c.) motors are advantageous for a number of uses, but are not desirable for home appliances and other applications where direct or three phase (a.c.) current is not available without trouble and/or expense. However, many alternating current (a.c.) motors of known types are not generally readily able to produce powerful, rapidly reversing motion continuously, especially motion characterized by high starting and low rotational speed torque. Likewise, conventional motors, especially those having starting shunt windings and the like, generally draw very heavy current when they are started, and such motors therefore cannot generally be continuously operated in the starting mode, as would be called for by their use to preclude rapidly oscillating motion.
Other typical special purpose alternating current motors include the type used in a watt-hour meter, wherein a current winding and separate voltage winding only are used, and wherein the principle of operation is that of an eddy current motor. However, such motors do not produce appreciable torque at any speed.
Since one purpose of the present invention is to provide a motor which can operate directly as part of an oscillatable mechanism such as a washing machine agitator, it is necessary that a satisfactory motor for this purpose be able to be reversed continuously, occasionally stalled, and still be free from adverse effects. Thus, for example, it is recognized that there would be significant advantages in driving certain mechanisms directly, such as washing machine agitators and spin baskets, in which the oscillating motion required could be supplied directly from the motor rather than through a complex transmission which would otherwise by necessary to bring about the desired movement cycle. However, producing such motion directly is either not possible with heretofore available electric motors, or where possible, is of reduced efficiency.
Accordingly, an object of the present invention is to provide an electric motor of an improved design.
A further object is to provide an electric motor having relatively low rotor inertia and which is free from undesirable angular torque variations, sometimes manifested as so-called "cogging" or "wow".
A further object is the provision of an electric motor which may be continually oscillated and even stalled without developing undue heat and without drawing excessive current from the line circuit with which it is associated.
Another object is to provide a motor which is easily controllable through a wide range of speeds and torque loadings, particularly a motor which is free of negative torque and speed relational characteristics.
A further object is the provision of a motor which would exhibit such characteristics throughout a relatively broad operating speed band or spectrum.
Another object is the provision of a motor wherein relatively high torque may be generated directly even with a rotor having a fairly compact outside diameter.
Still another object is the provision of a motor wherein the windings are able to produce high force density.
A still further object is the provision of a motor which does not depend for its operation upon the generation of back electromotive forces created solely or principally in response to rotor or armature speed.
Another object is to provide an electric motor wherein the speed and torque outputs are relatively closely proportional to the voltage applied to the motor and which consequently is operable over a wide applied voltage range without loss of operating effectiveness.
Another object is the provision of a motor wherein current draw is largely limited by the inherent impedence of the circuits rather than by generated back electromotive forces ("e.m.f.'s.").
Another object is the provision of a motor wherein the movable elements are free from iron, with the result that variable counter e.m.f.'s and undesirable voltage harmonic frequencies are not generated to a perceptible extent.
A still further object is the provision of a motor whose relatively open construction provides for efficient heat dissipation.
A still further object is to provide a motor of the desired characteristics which will operate on commonly available household current.
Another object is the provision of a motor which may have a higher torque in one direction of rotation compared to its torque in the opposite rotational direction.
A still further object is to provide a motor whose torque can be varied by means of a switchably varied capacitance.
The present invention achieves these objects, and other inherent objects and advantages thereof by providing an electric motor having a drive shaft adapted to be rotated by a rotor unit in the form of a generally flat disc axially spaced from and passing in use closely adjacent the surface of pole pieces of an annular segmented configuration stator assembly and containing distributed multi-phase windings in slots formed therein. The windings for each pole being distributed in two or more pairs of slots.
The exact manner in which these objects and other inherent objects and advantages of the invention are accomplished will more easily be understood when reference is made to the accompanying detailed description of the preferred embodiments of the invention and to the accompanying drawings wherein like reference numerals indicate correspondng parts throughout.